Group development is a unique type of research that actually enables you to learn more about group behavior as time passes by. This particular research is done simply by examining change patterns and continuity in a group. It is quite hard however to determine how much certain changes affect a group, but there are quite a few methods and models that help you determine those things a little easier.
One of the first, and still the most popular study regarding group development must surely be the Kurt Lewin's individual change model. This is the first model that introduced the group dynamics, and how changes in groups affect the whole team in one way or another.
Kurt Lewin has also used this particular model to implement a lot of other ideas as well, which include quasi-stationary equilibrium, as well as mutual and cross-level influence.
One of the first models he created regarding individual change stated that there are 3 steps in the whole group development process, those being unfreezing, change and freezing.
The unfreezing process is basically requiring group members to dismantle the existing mind set and avoiding the defense mechanisms. After all, the whole idea is to do all in your power to start the change in an individual fashion, and then expand it to other people in your group as well.
The second stage is the most complex one and includes the overall change. Most of the time, this will be the period when the group members become accommodated with the changes, or they are undergoing a transition from new to old habits.
In the last stage, named the freezing process, the new ideas are already introduced in the new group mindset, and the people are just trying to familiarize with them.
The individual change model created by Kurt Lewin provides people with the best way of actually seeing the phases people go through during the group development period. Yes, they might be a little harder to spot when you actually go through them, but there are normal things that every group goes through. However, Kurt Lewin's theory captures all the important aspects of this transgression, and it is widely accepted as one of the important group development models in the world.